The present invention relates to a plant nucleic acid which confers resistance to plants to Tospoviruses, and uses thereof.
Tospoviruses are thrips-transmitted viruses that belong to the genus Tospovirus (family Bunyaviridae) and cause substantial yield loss to ornamental and vegetable crops in several areas of the world (German et al., xe2x80x9cTospoviruses: Diagnosis, Molecular Biology, Phylogeny, and Vector Relationships,xe2x80x9d Annu. Rev. of Phytopathol 30:315-348 (1992); Peters et al., xe2x80x9cVector Relations in the Transmission and Epidemiology of Tospoviruses. In: International Symposium on Tospoviruses and Thrips of Floral and Vegetable Crops,xe2x80x9d Acta Horticulturae 431:29-42 (1996)). The members of this genus are characterized by a genome comprised of three separate single stranded RNAs (S, M, and L RNAs) enveloped in a lipidic membrane and associated with two glycoproteins, G1 and G2 (German et al., xe2x80x9cTospoviruses: Diagnosis, Molecular Biology, Phylogeny, and Vector Relationships,xe2x80x9d Annu. Rev. of Phytopathol 30:315-348 (1992); van Poelwijk et al., xe2x80x9cReplication and Expression of the Tospovirus Genome. Proceedings of the International Symposium on Tospovirus and Thrips of Floral and Vegetable Crops,xe2x80x9d Acta Horticulturae 431:201-208 (1996)). Based on serological properties, vector specificity, host range, and nucleotide and amino acid sequences of the nucleoprotein gene, several species have been established in the genus Tospovirus (de xc3x81vila et al., xe2x80x9cClassification of Tospoviruses Based on Phylogeny of Nucleoprotein Gene Sequences,xe2x80x9d J. Gen. Virol 74:153-159 (1993); Goldbach et al., xe2x80x9cIntroduction. In: International Symposium on Tospoviruses and Thrips of Floral and Vegetable Crops,xe2x80x9d Acta Horticulturae 431:21-26 (1996); Peters et al., xe2x80x9cVector Relations in the Transmission and Epidemiology of Tospoviruses. In: International Symposium on Tospoviruses and Thrips of Floral and Vegetable Crops,xe2x80x9d Acta Horticulturae 431:29-42 (1996)). Tomato spotted wilt virus (TSWV), tomato chlorotic spot virus (TCSV), impatiens necrotic spot virus (INSV), and groundnut ringspot virus (GRSV) are the Tospovirus species commonly associated with important yield losses in the tomato crop. TSWV, the type species of the genus, has a worldwide distribution, whereas GRSV and TCSV have, thus far, only been identified on tomatoes grown in Brazil and Argentina (Dewey et al., xe2x80x9cMolecular Diversity of Tospovirus in Argentina: A Summary. In: International Symposium on Tospoviruses and Thrips of Floral and Vegetable Crops,xe2x80x9d Acta Horticulturae 431:261-263 (1996); Peters et al., xe2x80x9cVector Relations in the Transmission and Epidemiology of Tospoviruses. In: International Symposium on Tospoviruses and Thrips of Floral and Vegetable Crops,xe2x80x9d Acta Horticulturae 431:29-42 (1996); Resende et al., xe2x80x9cNew Tospovirus Species Found in Brazil. In: International Symposium on Tospoviruses and Thrips of Floral and Vegetable Crops,xe2x80x9d Acta Horticulturae 431:78-89 (1996)). In Brazil, new tospovirus species that infect tomato are also being characterized (Resende et al., xe2x80x9cNew Tospovirus Species Found in Brazil. In: International Symposium on Tospoviruses and Thrips of Floral and Vegetable Crops,xe2x80x9d Acta Horticulturae 431:78-89 (1996)).
Because genetic resistance offers the best means of protecting crop plants against tospovirus infection, considerable effort has been devoted to the development of resistant varieties (Cho et al., xe2x80x9cConventional Breeding: Host-Plant Resistance and the Use of Molecular Markers to Develop Resistance to Tomato Spotted Wilt Virus in Vegetables. In: International Symposium on Tospoviruses and Thrips of Floral and Vegetable Crops,xe2x80x9d Acta Horticulturae 431:367-378 (1996); Rosellxc3x3 et al., xe2x80x9cGenetics of Tomato Spotted Wilt Virus Resistance Coming From Lycopersicon peruvianum,xe2x80x9d Eur. J. of Plant Path. 104:499-509 (1998)). Naturally occurring host resistance to tospoviruses has been reported in many Lycopersicon species (Finlay, xe2x80x9cInheritance of Spotted Wilt Resistance in Tomato. II. Five Genes Controlling Spotted Wilt Resistance in Four Tomato Types,xe2x80x9d Aust. J. Biol. Sci. 6:153-163 (1953); Cho et al., xe2x80x9cConventional Breeding: Host-Plant Resistance and the Use of Molecular Markers to Develop Resistance to Tomato Spotted Wilt Virus in Vegetables. In: International Symposium on Tospoviruses and Thrips of Floral and Vegetable Crops,xe2x80x9d Acta Horticulturae 431:367-378 (1996); Krishna Kumar et al., xe2x80x9cEvaluation of Lycopersicum Germplasm for Tomato Spotted Wilt Tospovirus Resistance by Mechanical and Thrips Transmission,xe2x80x9d Plant Dis. 77:938-941 (1993); Paterson et al., xe2x80x9cResistance in Two Lycopersicon Species to an Arkansas Isolate of Tomato Spotted Wilt Virus,xe2x80x9d Euphytica 43:173-178 (1989); Rosellxc3x3 et al., xe2x80x9cViral Diseases Causing the Greatest Economic Losses to the Tomato Crop. I. The Tomato Spotted Wilt Virusxe2x80x94A Review,xe2x80x9d Scientia Horticulturae 67:117-150 (1996); Stevens et al., xe2x80x9cEvaluation of Seven Lycopersicon Species for Resistance to Tomato Spotted Wilt Virus (TSWV),xe2x80x9d Euphytica 80:79-84 (1994)). However, in many cases, this resistance is species and/or isolate specific and therefore not very useful for breeding purposes. Broad spectrum tospovirus resistance was found in the L. esculentum cultivar xe2x80x98Stevensxe2x80x99 (van Zijl et al., xe2x80x9cBreeding Tomatoes for Processing in South Africa,xe2x80x9d Acta Horticulturae 194:69-75 (1986)). The TSWV resistance of this cultivar, introgressed from an unknown L. peruvianum accession, is conferred by a single gene, Sw-5, which is incompletely dominant (Stevens et al., xe2x80x9cInheritance of a Gene for Resistance to Tomato Spotted Wilt Virus (TSWV) From Lycopersicon peruvianum Mill,xe2x80x9d Euphytica 59:9-17 (1992)). This gene also seems to provide resistance to TCSV and GRSV (Boiteux et al., xe2x80x9cGenetic Basis of Resistance Against Two Tospovirus Species in Tomato (Lycopersicon esculentum),xe2x80x9d Euphytica 71:151-154 (1993)).
Genes conferring resistance to different isolates of the same pathogen or different pathogens are often organized in the plant genome as tandem arrays of homologues (Hammond-Kosack et al., xe2x80x9cPlant Disease Resistance Genes,xe2x80x9d Annu. Rev. Plant Physiol. Plant Mol. Biol. 48:575-607 (1997)). Therefore, the multiple resistances conferred by Sw-5 raise the question of whether the Sw-5 locus consists of a cluster of tightly linked genes, each gene having its own virus specificity, or whether it encodes a single gene product capable of recognizing several tospovirus isolates and species. In addition, the physiological mechanism by which Sw-5 provides resistance is unclear. In tomato plants carrying Sw-5, the virus cannot spread systemically throughout the plant; and, in many cases, the inoculated leaves do not show any macroscopic symptoms. However, for some tospovirus isolates and/or under high inoculum pressure, local and systemic necrotic lesions appear on the inoculated plants, suggesting that Sw-5 resistance can elicit a hypersensitive response (Stevens et al., xe2x80x9cInheritance of a Gene for Resistance to Tomato Spotted Wilt Virus (TSWV) From Lycopersicon peruvianum Mill,xe2x80x9d Euphytica 59:9-17 (1992); Brommonschenkel et al., xe2x80x9cMap-based Cloning of the Tomato Genomic Region that Spans the Sw-5 Tospovirus Resistance Gene in Tomato,xe2x80x9d Mol. Gen. Genet. 256:121-126 (1997); Rosellxc3x3 et al., xe2x80x9cGenetics of Tomato Spotted Wilt Virus Resistance Coming From Lycopersicon peruvianum,xe2x80x9d Eur. J. of Plant Path. 104:499-509 (1998)). Sw-5 may also be developmentally regulated, as the resistance gene does not appear to provide tospovirus resistance in tomato fruits (de Haan et al., xe2x80x9cTransgenic Tomato Hybrids Resistant to Tomato Spotted Wilt Virus Infection. In: International Symposium on Tospoviruses, and Thrips of Floral and Vegetable Crops,xe2x80x9d Acta Horticulturae 431:417-426 (1996)).
These unusual characteristics of Sw-5 and its tight linkage to RFLP marker CT220 on the long arm of tomato chromosome 9 led to the isolation of this gene via map-based cloning. By high resolution-genetic linkage analysis of Sw-5 recombinant plants and chromosome walking, it was demonstrated that the Sw-5 locus resides in a 100 kb genomic region spanned by 10 overlapping plant transformation-competent cosmid clones (Brommonschenkel et al., xe2x80x9cMap-based Cloning of the Tomato Genomic Region that Spans the Sw-5 Tospovirus Resistance Gene in Tomato,xe2x80x9d Mol. Gen. Genet 256:121-126 (1997); Tanksley et al, xe2x80x9cHigh Density Molecular Linkage Maps of the Tomato and Potato Genomes,xe2x80x9d Genetics 132:1141-1160 (1992)).
Tospoviruses causes substantial yield losses to ornamental and vegetable crops worldwide. TSWV is especially damaging to tomatoes in South America, Africa, and certain parts of Asia. No genes conferring resistance to this virus have been isolated. It would be useful to have a Tospovirus resistance gene in order to engineer virus resistant tomatoes and other crops.
The present invention is directed to overcoming this and related deficiencies in the art.
The present invention relates to an isolated plant nucleic acid molecule which imparts resistance in plants to Tospoviruses.
The present invention also relates to a protein, which may be purified or recombinant, which is encoded by the isolated nucleic acid of the present invention.
The present invention also relates to a method of imparting to a plant resistance to a Tospovirus which involves transforming a plant with a nucleic acid molecule under conditions effective to impart to the plant resistance to a Tospovirus.
The present invention also relates to a method of eliciting a hypersensitive response in a plant. This involves providing a transgenic plant which has been transformed with a nucleic acid molecule which imparts resistance in plants to Tospoviruses, and expressing the nucleic acid under conditions to elicit a hypersensitive response in the plant.